The present invention relates to a lock mechanism for locking a movable member relative to a base member against a force of urging means. The lock mechanism is a push and push type (also referred to as a push-lock and push-open type) in which the movable member is locked through a first pushing operation and is released through the next pushing operation. The present invention also relates to a opening-closing device of a movable member with the lock mechanism.
Japanese Patent No. 3,126,992 has disclosed a lock mechanism including a striker provided on one of a movable member and a base member, and a latching device provided on the other of the movable member and the base member. The latching device includes a latching member with a swing groove, a spring member, and a pin. FIGS. 8(a)–8(c) show another structure including a cam provided on one of the movable member and the base member and having a swing groove; and a swing member movably provided on the other of the movable member and the base member and including a pin for tracing the swing groove. The latter mechanism is superior to the former due to a smaller number of components and a lower switching noise.
Patent reference 1 has disclosed a lock mechanism shown in FIG. 8(a). In the lock mechanism, a movable member (box) rotates in a vertical direction relative to a base member (case on a ceiling side of a car compartment). An upper end of a swing member 60 is supported on the base member through an axis 62, and a pin 61 projects at a lower end of the swing member 60. A cam 50 is provided on the movable member, and a swing groove 51 is formed around a roughly heart-shaped projecting portion 52. The swing groove 51 includes a guide groove 51a extending to a lower right side from an upper side; a guide groove 51b and a guide groove 51d situated below the guide groove 51a; an engagement groove 51c located at an upper side between the guide grooves 51b and 51d; and a return groove 51e extending to an upper side from the guide groove 51d. 
When the movable member is pushed to rotate toward the base member with the cam 50 against an urging force, the pin 61 moves to the guide groove 51b from the guide groove 51a. When the movable member is released, the pin 61 moves from the guide groove 51b to the engagement groove 51c. When the movable member is pushed and released again, the pin 61 moves from the engagement groove 51c to the guide groove 51d, and enters the return groove 51e. As a result, the movable member is switched in a direction away from the base member through the urging force and its own weight. In the lock mechanism, the swing member 60 is in a suspended state and moves right and left around the axis 62, so that the pin 61 does not receive an excessive load.
Patent reference 2 has disclosed a lock mechanism shown in FIG. 8(b). In the lock mechanism, a movable member (inner case such as an ashtray) is rotated relative to the base member (outer case mounted to a car chamber panel). A swing member (lock main member) 65 includes a first elastic portion 67 supported on the base member through an axis 66 at a lower end; a second elastic portion 68 extending toward both sides above the elastic portion 67; and a pin 69 projecting at an upper end. A cam 55 is provided on the movable member and includes a swing groove 56 around a roughly heart-shaped projecting portion 57. The swing groove 56 includes a guide groove for introduction, a guide groove for engagement, a guide groove for release, an engagement groove, and a return groove (reference numerals omitted). The movable member is locked and released through a process same as that of the lock mechanism shown in FIG. 8(a). In the lock mechanism, the first elastic portion 67 is urged to press the pin 69 against a slope of the engagement groove, and the second elastic portion 68 is urged to press the pin 69 against a slope of the return groove through the swing member 65, respectively. Accordingly, it is possible to stably maintain the lock mechanism in an engagement state and prevent an excessive movement of the swing member 65.    Patent reference 1; Japanese Patent Publication (Kokai) No. 11-245733    Patent reference 2; Japanese Patent Publication (Kokai) No. 07-215117
In the lock mechanisms described above, the swing members 60 and 65 are provided on the base member, and the cams 50 and 55 are provided on the movable member. It is also possible to provide the swing members and the cams in the opposite way. Depending on shapes and sizes of the base member and the movable member, when the swing member is provided on the base member, the lock mechanism becomes complicated. In some cases, it is easier to simplify the lock mechanism when the cam is provided on the base member.
However, the conventional lock mechanisms have the following problems when the swing member is provided on the movable member. First, it is necessary to movably support the swing member for securing a smooth movement of the pin. Considering its own weight, it is necessary to arrange the swing member at a certain position relative to the movable member.
FIG. 8(c) is a schematic view of a modified version of the lock mechanism shown in FIG. 8(a), in which the cam 50 is provided on the base member, and the swing member 60 is provided on the movable member. The swing member 60 rotates along with the movable member around the axis 62. Accordingly, when the pin 61 moves from the guide groove 51b to the engagement groove 51c, the swing member 60 reenters the guide groove 51a through the guide groove 51b by the weight of the swing member 60, i.e. a downward momentum, thereby preventing a normal operation. In a case of the structure shown in FIG. 8(b), the swing member 65 becomes complicated due to the elastic portions 67 and 68. It is also difficult to provide a contacting portion on the movable member for receiving the elastic portions 67 and 68, thereby limiting a space for installation.
In view of the problems described above, an objective of the present invention is to provide a lock mechanism with a simple arrangement and a minimum installation space even when a swing member is provided on a movable member, thereby preventing a wrong operation of a pin and making a design flexible.
Further objects and advantages of the invention will be apparent from the following description of the invention.